2022-08-17 19:05:59

by William McVicker

Subject: [PATCH v2] PCI/PM: Switch D3Hot delay to also use usleep_range

From: Sajid Dalvi <[email protected]>

Since the PCI spec requires a 10ms D3Hot delay (defined by
PCI_PM_D3HOT_WAIT) and a few of the PCI quirks update the D3Hot delay up
to 120ms, let's add support for both usleep_range and msleep based on
the delay time to improve the delay accuracy.

This patch is based off of a commit from Sajid Dalvi <[email protected]>
in the Pixel 6 kernel tree [1]. Testing on a Pixel 6, found that the
10ms delay for the Exynos PCIe device was on average delaying for 19ms
when the spec requires 10ms. Switching from msleep to uslseep_range
therefore decreases the resume time on a Pixel 6 on average by 9ms.

[1] https://android.googlesource.com/kernel/gs/+/18a8cad68d8e6d50f339a716a18295e6d987cee3

Signed-off-by: Sajid Dalvi <[email protected]>
Signed-off-by: Will McVicker <[email protected]>
---
drivers/pci/pci.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 95bc329e74c0..97a042ca9032 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -63,16 +63,26 @@ struct pci_pme_device {
};

#define PME_TIMEOUT 1000 /* How long between PME checks */
+#define MAX(a, b) ((a) >= (b) ? (a) : (b))

static void pci_dev_d3_sleep(struct pci_dev *dev)
{
- unsigned int delay = dev->d3hot_delay;
+ unsigned int delay_ms = dev->d3hot_delay;

- if (delay < pci_pm_d3hot_delay)
- delay = pci_pm_d3hot_delay;
+ if (delay_ms < pci_pm_d3hot_delay)
+ delay_ms = pci_pm_d3hot_delay;

- if (delay)
- msleep(delay);
+ if (delay_ms) {
+ if (delay_ms <= 20) {
+ /* Use a 20-25% upper bound with 1ms minimum */
+ unsigned int upper = MAX((delay_ms >> 3) << 1, 1);
+
+ usleep_range(delay_ms * USEC_PER_MSEC,
+ (delay_ms + upper) * USEC_PER_MSEC);
+ } else {
+ msleep(delay_ms);
+ }
+ }
}

bool pci_reset_supported(struct pci_dev *dev)

base-commit: 274a2eebf80c60246f9edd6ef8e9a095ad121264
--
2.37.1.595.g718a3a8f04-goog

2022-08-17 19:36:16

by Matthias Kaehlcke

Subject: Re: [PATCH v2] PCI/PM: Switch D3Hot delay to also use usleep_range

Hi Will,

On Wed, Aug 17, 2022 at 06:52:02PM +0000, Will McVicker wrote:
> From: Sajid Dalvi <[email protected]>
>
> Since the PCI spec requires a 10ms D3Hot delay (defined by
> PCI_PM_D3HOT_WAIT) and a few of the PCI quirks update the D3Hot delay up
> to 120ms, let's add support for both usleep_range and msleep based on
> the delay time to improve the delay accuracy.
>
> This patch is based off of a commit from Sajid Dalvi <[email protected]>
> in the Pixel 6 kernel tree [1]. Testing on a Pixel 6, found that the
> 10ms delay for the Exynos PCIe device was on average delaying for 19ms
> when the spec requires 10ms. Switching from msleep to uslseep_range
> therefore decreases the resume time on a Pixel 6 on average by 9ms.
>
> [1] https://android.googlesource.com/kernel/gs/+/18a8cad68d8e6d50f339a716a18295e6d987cee3
>
> Signed-off-by: Sajid Dalvi <[email protected]>
> Signed-off-by: Will McVicker <[email protected]>
> ---
> drivers/pci/pci.c | 20 +++++++++++++++-----
> 1 file changed, 15 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 95bc329e74c0..97a042ca9032 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -63,16 +63,26 @@ struct pci_pme_device {
> };
>
> #define PME_TIMEOUT 1000 /* How long between PME checks */
> +#define MAX(a, b) ((a) >= (b) ? (a) : (b))

no need to define this macro, you can use max() from
include/linux/minmax.h instead.

>
> static void pci_dev_d3_sleep(struct pci_dev *dev)
> {
> - unsigned int delay = dev->d3hot_delay;
> + unsigned int delay_ms = dev->d3hot_delay;
>
> - if (delay < pci_pm_d3hot_delay)
> - delay = pci_pm_d3hot_delay;
> + if (delay_ms < pci_pm_d3hot_delay)
> + delay_ms = pci_pm_d3hot_delay;

nit: since you are already touching this code you could change it to:

unsigned int delay_ms = max(dev->d3hot_delay, pci_pm_d3hot_delay);

>
> - if (delay)
> - msleep(delay);
> + if (delay_ms) {
> + if (delay_ms <= 20) {
> + /* Use a 20-25% upper bound with 1ms minimum */
> + unsigned int upper = MAX((delay_ms >> 3) << 1, 1);

Not sure this optimization of using bit shifts instead of the clearer do_div()
is really needed here. pci_dev_d3_sleep() is not a super hot code path IIUC.

> +
> + usleep_range(delay_ms * USEC_PER_MSEC,
> + (delay_ms + upper) * USEC_PER_MSEC);
> + } else {
> + msleep(delay_ms);
> + }
> + }
> }
>
> bool pci_reset_supported(struct pci_dev *dev)
>
> base-commit: 274a2eebf80c60246f9edd6ef8e9a095ad121264
> --
> 2.37.1.595.g718a3a8f04-goog
>

2022-08-17 20:24:54

by William McVicker

Subject: Re: [PATCH v2] PCI/PM: Switch D3Hot delay to also use usleep_range

On 08/17/2022, Matthias Kaehlcke wrote:
> Hi Will,
>
> On Wed, Aug 17, 2022 at 06:52:02PM +0000, Will McVicker wrote:
> > From: Sajid Dalvi <[email protected]>
> >
> > Since the PCI spec requires a 10ms D3Hot delay (defined by
> > PCI_PM_D3HOT_WAIT) and a few of the PCI quirks update the D3Hot delay up
> > to 120ms, let's add support for both usleep_range and msleep based on
> > the delay time to improve the delay accuracy.
> >
> > This patch is based off of a commit from Sajid Dalvi <[email protected]>
> > in the Pixel 6 kernel tree [1]. Testing on a Pixel 6, found that the
> > 10ms delay for the Exynos PCIe device was on average delaying for 19ms
> > when the spec requires 10ms. Switching from msleep to uslseep_range
> > therefore decreases the resume time on a Pixel 6 on average by 9ms.
> >
> > [1] https://android.googlesource.com/kernel/gs/+/18a8cad68d8e6d50f339a716a18295e6d987cee3
> >
> > Signed-off-by: Sajid Dalvi <[email protected]>
> > Signed-off-by: Will McVicker <[email protected]>
> > ---
> > drivers/pci/pci.c | 20 +++++++++++++++-----
> > 1 file changed, 15 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > index 95bc329e74c0..97a042ca9032 100644
> > --- a/drivers/pci/pci.c
> > +++ b/drivers/pci/pci.c
> > @@ -63,16 +63,26 @@ struct pci_pme_device {
> > };
> >
> > #define PME_TIMEOUT 1000 /* How long between PME checks */
> > +#define MAX(a, b) ((a) >= (b) ? (a) : (b))
>
> no need to define this macro, you can use max() from
> include/linux/minmax.h instead.
>
> >
> > static void pci_dev_d3_sleep(struct pci_dev *dev)
> > {
> > - unsigned int delay = dev->d3hot_delay;
> > + unsigned int delay_ms = dev->d3hot_delay;
> >
> > - if (delay < pci_pm_d3hot_delay)
> > - delay = pci_pm_d3hot_delay;
> > + if (delay_ms < pci_pm_d3hot_delay)
> > + delay_ms = pci_pm_d3hot_delay;
>
> nit: since you are already touching this code you could change it to:
>
> unsigned int delay_ms = max(dev->d3hot_delay, pci_pm_d3hot_delay);
>
> >
> > - if (delay)
> > - msleep(delay);
> > + if (delay_ms) {
> > + if (delay_ms <= 20) {
> > + /* Use a 20-25% upper bound with 1ms minimum */
> > + unsigned int upper = MAX((delay_ms >> 3) << 1, 1);
>
> Not sure this optimization of using bit shifts instead of the clearer do_div()
> is really needed here. pci_dev_d3_sleep() is not a super hot code path IIUC.
>
> > +
> > + usleep_range(delay_ms * USEC_PER_MSEC,
> > + (delay_ms + upper) * USEC_PER_MSEC);
> > + } else {
> > + msleep(delay_ms);
> > + }
> > + }
> > }
> >
> > bool pci_reset_supported(struct pci_dev *dev)
> >
> > base-commit: 274a2eebf80c60246f9edd6ef8e9a095ad121264
> > --
> > 2.37.1.595.g718a3a8f04-goog
> >

Thanks for the suggestions! I'll update those in the next patchset.

--Will